The present invention relates to an electric starter for starting an internal combustion engine, and particularly relates to an improved actuator for an electromagnetic switch, which moves the overrunning clutch of an electric starter.
FIG. 4 shows a longitudinally sectional view of a conventional electric starter 1 comprising a dc motor 2, a front bracket 3, an output rotary shaft 4, an overrunning clutch 5, helical splines 6, a splined tube 7, a pinion 8, a shift lever 9, and an electromagnetic switch 10. The output rotary shaft 4 is supported by a bearing 3a fitted in the front bracket 3 and is integrally conjoined to the front end of the armature shaft 2a of the dc motor 2. The overrunning clutch 5 is fitted on the output rotary shaft 4 so that the clutch is slidable in the axial direction thereof. The helical splines 6 are formed on the output rotary shaft 4. The splined tube 7 is integrally conjoined to the outer member 5a of the clutch 5 and engaged with the helical splines 6 to transmit the torque of the output rotary shaft 4 to the outer member of the clutch. The pinion 8 is integrally formed on the inner member 5b of the clutch 5. The shift lever 9 is engaged at the lower end thereof with the splined tube 7 and at the upper end thereof with a pin 12 attached to the actuator 11 of the electromagnetic switch 10 provided at the peripheral portion of the dc motor 2. The shift lever 9 is swingable about the fulcrum portion 13 thereof. A spring 14 is provided in the actuator 11 to push the pinion 8 onto the ring gear of an engine (which is not shown in the drawing) when the pinion is engaged with the ring gear.
When the electric starter is put into action, the electromagnetic switch 10 is electrically energized so that the actuator 11 is magnetically attracted to swing the shift lever 9 about the fulcrum portion 13 to move the upper end of the lever backward (leftward as to FIG. 4), and the lower end thereof forward (rightward as to FIG. 4). As a result, the overrunning clutch 5 is moved forward on the output rotary shaft 4 and the pinion 8 is engaged with the ring gear of the engine to start it.
However, since the actuator 11 of the electromagnetic switch 10 has an internal opening in which the spring 14 is provided, the effective cross-sectional area of the magnetism passage of the actuator is so small that the magnetic attractive force of the switch is not high enough to properly swing the shift lever 9. This is a problem.